The smell of cat permeated the house and my mother said we had no mice in the house that year.Does the fact this mouse was found dead make a difference?

The white areas on the wall are where pictures were hung and the wall surfaces underneath the pictures were protected against nicotine stains.  

In 18-months the damage will be somewhat limited and {hopefully} will not have had the opportunity to permeate the subfloor and structure {though that is a possibility} - you may just get away with a lots of cleaning and replacing finish flooring (like carpets).The longer they stay, the more expensive the repairs will be at move out.

Basically the only thing we didn't charge tenant for was painting, and we did charge paint fee if there was nicotine stained walls.

In-ground tanks can leak for years and years and no one notices until lots of oil has permeated the soil.

SMOKE,, Nicotine,, not easy,, harder than you think..Basics..1.

In my house when the walls are sprayed with ammonia the brown tar and nicotine run down the wall.  

You have damage all throughout the kitchen; cabinets, floor, wall, behind the wall, ceiling, can't use the appliances, not to mention the smell of smoke that's permeated throughout. 

Will also cover the nicotine stains.  

In my experience, the only thing that truly works over nicotine staining and smoke smell is a true Shellac primer.